1. Field of the Invention
The present invention relates to a hydraulic system for a motor vehicle incorporating a pump suction enhancer therein for boosting operating oil flow into a suction port of an oil pump, and also relates to an oil reservoir provided bodily with the pump suction enhancer. It further relates to the pump suction enhancer for use in the hydraulic system or in combination with the oil reservoir.
2. Discussion of the Related Art
In a hydraulic system or circuit device for a motor vehicle, the oil flow discharged from a power steering oil pump tends to become larger with increase in number of function components or accessories such as a radiator cooling fan device, suspension control actuators and the like in addition to a power steering device. With the large discharge flow from the oil pump, it has been required to improve the suction of a large return oil flow into the oil pump in order to prevent cavitation from occurring at the suction passage to the oil pump.
In a hydraulic system of this kind, as described in U.S. Pat. No. 5,802,848 to McClendon et al., a power steering pump draws operating oil from a reservoir and supplies a constant volume of the operating oil to a fluid motor for a radiator cooling fan device through a main conduit. At the downstream of the radiator cooling fan device, the main conduit is divided by a flow divider into a low flow conduit leading to the reservoir through a steering assist fluid motor (i.e., power steering device) and a high flow conduit bypassing the steering assist fluid motor to lead to the reservoir. Thus, a large volume of the operating oil is returned to the reservoir after the use for driving the radiator cooling fan device, while a small volume of the operating oil is used for driving the steering assist motor before being returned to the reservoir. Further, means for boosting the suction of the operating oil into a suction port of the power steering pump is incorporated in an internal chamber of the reservoir and is submerged in the operating oil in the chamber. The means for boosting the suction includes a venturi tube passage and a nozzle which are arranged so that the large volume of the operating oil returned from the high flow conduit is ejected from the nozzle into the venturi tube passage thereby to boost the suction of the operating oil to a passage connected to the suction port of the power steering pump.
However, in the known hydraulic system, the means for boosting the suction is incorporated submerged in the reservoir, and the reservoir itself is provided bodily with the power steering pump. Thus, a problem arises in that substantial restraint is imposed on the place where the pump and reservoir combination is arranged. That is, the place where the pump and reservoir combination can be arranged is determined in dependence on the arrangement in an engine room of mechanical units and components such as an engine, a power steering device, a brake booster device, a battery, a radiator, etc. In some cases, the pump and reservoir combination may be arranged close to the power steering device but may be too far from the radiator cooling fan device to use a conduit of an adequate length which is designed against vibration, pulsation and other adverse causes. In this case, an oil pump and an oil reservoir may not be used in integration and may rather be arranged at respective places separated from, and independently of, each other. This problem becomes more serious in the case that the number of accessories such as radiator cooling fan device, suspension control actuators and the like increases.
Another known hydraulic system of this kind is described in U.S. Pat. No. 5,943,861 to Davison et al., wherein an oil reservoir is provided separated from a power steering pump and wherein means for boosting the suction of the operating oil into a suction port of the power steering pump is incorporated in the reservoir to extend across an internal chamber of the same. The means for boosting the suction is composed of a venturi tube passage and a nozzle which are arranged in the internal chamber of the reservoir to extend diametrically of the same in alignment. Therefore, the venturi tube passage and the nozzle have to be assembled inside of the reservoir. This disadvantageously makes the assembling work for the oil reservoir complicated and troublesome and also makes the maintenance or check of the boosting means substantially impossible.